A probe of the general construction mentioned above is for instance known in the art from the document DE 297 01 652 U1. This probe operates without a carrier gas. An exchange of the gas within the measuring space with the environment takes place via a defined small exchange opening to the atmosphere in the otherwise enclosed measuring space. Thus, the gas exchange is mainly diffusion controlled. This results in rather long response times for obtaining constant readings, if the concentration of the volatile component in the solution changes, because the time period for achieving the total transport rate equilibrium is determined by the diffusion through the exchange opening and depends on the time for obtaining a steady state equilibrium diffusion rate.
From the documents EP 0 174 417 B1 and DE-199 59 271 A1 a probe device is known, which is useful for measuring on-line, e.g. in-line. The measuring space is sealed against the solution by a permeation membrane formed as a tube, which tightly encloses a probe finger and covers an opening in the probe finger to the measuring space. This probe device is operated using a carrier gas. Probe devices of this general design have proved to work well, but it appears desirable to still reduce response times upon concentration changes of the volatile component in the solution. Further, it appears desirable to provide a probe device which may be made and operated in a more simple manner.
In all probe devices known in the art the response time, in particular the dead time, is at least several seconds and, thus, improvement is needed.